Is Glenn Greenwald holding back any information?

A fair question raised in the Washington Post, regarding The Guardian's Glenn Greenwald:

Edward Wasserman, dean of the University of California at Berkeley’s journalism school, said having a “social commitment” doesn’t disqualify anyone from being a journalist. But the public should remain skeptical of reporters who are also advocates. “Do we know if he’s pulling his punches or has his fingers on the scale because some information that should he should be reporting doesn’t fit [with his cause]?” Wasserman asked in an interview. “If that’s the case, he should be castigated.”

Greenwald, an outspoken civil liberties advocate, was the first journalist to report on the National Securtiy Agency's monitoring of U.S. citizens' phone records. Since then, he has been a high-profile critic of the Obama administration's surveillance techniques. He was also highly critical of the Bush (43) administration.